Acute liver failure (ALF) is characterized by severe and sudden liver cell dysfunction leading to coagulopathy and encephalopathy in previously healthy persons with no known underlying liver disease. ALF affects approximately 2,000 people/year in the United States from a variety of different etiologies, including acetaminophen, viral hepatitis, drug-induced liver injury and indeterminate causes. 33% of patients die as a result of complications of ALF;another 29% require liver transplantation (LT), producing an enormous strain on health care resources. Development of non-invasive biomarkers to predict clinical outcome and need for LT is a critical area of research in ALF. Apoptosis is profoundly deranged in ALF, but systematic analysis of serum apoptosis markers as a prognostic tool has not been conducted on a large ALF cohort. Using the NIDDK-funded U.S. ALF Study Group (ALFSG) serum and data repository, which has enrolled over 1,100 patients;we examined circulating apoptotic and antiapoptotic markers and correlated levels of these markers with clinical outcome in 67 patients with a variety of etiologies. We found levels of the apoptosis-associated proteins TNF-a, HGF, IL-6 and M-30 antigen were at least 10-fold greater in ALF patients compared to patients with chronic HCV or normal controls, and that levels of sFas, TNF-a and HGF were all significantly higher in patients who died from ALF. High early levels of sFas and HGF appeared to be characteristic of drug-induced liver injury (DILI). Finally, levels of the liver-specific apoptosis marker M-30 antigen were significantly higher in patients who died or needed liver transplantation than those who survived spontaneously. With these promising pilot data, we therefore propose to develop a prediction rule for prognosis in ALF based on serum apoptotic markers in an extended cohort of patients with ALF. We will initially evaluate serum M-30 antigen, sFas, and HGF as unique predictors of outcome in a large subset (n =250) of ALFSG patients, and will then combine these data with known clinical variables to develop a clinical prediction rule. We will also evaluate the ability of serum sFas and HGF to predict etiology of AL. Finally, we will study the ability of changes in M-30 antigen to predict outcome in patients who recently completed a randomized, controlled trial of IV N-acetyl cysteine. The finding that serum apoptosis markers correlate broadly with clinical outcome and etiology will not only provide novel biomarkers for assessing clinical prognosis, but also will offer strong rationale for clinical trials of caspase and other apoptosis inhibitors and the use of these biomarkers to monitor clinical response in this devastating disorder. PUBLIC HEALTH RELEVANCE: Acute liver failure (ALF) is associated with high mortality and need for transplant. We have identified biomarkers in a smaller subset of the US ALF Study Group (ALFSG) that predicts outcome in ALF. We now propose to validate these tests in a much larger set of patients from the ALFSG.